Field of the Invention
The present invention relates to a semiconductor module having a configurable data width of an output bus, and to a housing configuration having such a semiconductor module.
Semiconductor modules such as semiconductor memory chips are used in various module configurations. The module configurations differ in particular in the number of data lines which are used and are connected to data connecting pads, so-called I/O pads, in order to achieve a system bus width of 64 or 72 bits. The data connecting pads are used for interchanging data between the module and a system controller. So-called x4, x8 and x16 module configurations exist, which use 4, 8 or 16 data lines per module for interchanging data.
For integration in a data processing system, semiconductor modules such as semiconductor memory chips are, for example, placed on a memory board (for example a so-called DIMM board) after being fitted into a housing (so-called package).
Currently used memory housings such as thin small outline package (TSOP) generally have a limited number of connecting pins, for example 54 or 66. The number of connecting pins is sufficient for present-day memory systems with a specified data and address bus topology, in order to connect 4, 8 or 16 bidirectional data lines with associated command and address lines.
If, by virtue of its basic configuration, a semiconductor module can be used in all x4, x8 and x16 module configurations and accordingly can be configured in the data width of at least one output bus, this results in that, if an x4 or x8 module configuration is provided, there are correspondingly unused connecting pins, so-called no-connects (NC), which are not electrically connected within the module. In general, all the connecting pins are used in an x16 module configuration. In this case, the achievable ratio of data connecting pads to connecting pads for connection of a ground potential (so-called signal-to-ground ratio) is normally 2:1. Therefore, two data connecting pads are associated with a common connecting pad for the positive supply voltage, and one connecting pad for a reference voltage (ground potential).
The effective overall inductance of a signal path is essentially governed by the series circuit formed by the inductance of the signal pin (that is to say the path from the driver via the pad, the bonding wire and the leadframe) and the effective inductance in the supply lines (that is to say the path from the supply connection of the driver to the supply pad, bonding wire and leadframe). If, for example, one driver is connected to two ground pins, the so-called return path inductance is approximately half as great as if it were connected via a single pin. If the ground connection is physically very close to the signal, the coupling inductance (so-called mutual inductance) is further reduced, or compensated for.
If, for example, one of the data connecting pads in an x4 or x8 module configuration is a no-connect, because that connecting pad is not used for interchanging data or commands, although this results in an improved signal-to-ground ratio, the achievable return path inductance is, however, restricted. In consequence, the maximum possible data transmission rate at which the data lines that are used can be operated is restricted.
The use of other mounting technologies (for example so-called chip scale or size packages (CSP) in ball grid arrays) makes it possible to use housing forms with an increased number of ground connecting pins while at the same time occupying less space on the board. In consequence, this can have a positive influence on the signal-to-ground ratio, hence reducing the inductance. Furthermore, housing forms such as these have less intrinsic inductance since their geometry is smaller and due to the use of appropriate materials. However, these housing forms are in general comparatively expensive to produce.
It is accordingly an object of the invention to provide a semiconductor module having a configurable data width of an output bus, and a housing configuration having a semiconductor module which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which data lines which are connected to data connecting pads can also be operated at a comparatively high frequency in a module configuration in which a reduced number of data lines are used.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor module having a configurable data width of at least one output bus. The semiconductor module contains data connecting pads, driver circuits each having an output connected to an associated one of the data connecting pads, and a connection for receiving an internal supply voltage for the semiconductor module. At least one of the data connecting pads not being used for interchanging data or commands during operation of the semiconductor module is permanently connected to the connection.
The semiconductor module according to the invention has data connecting pads and a connection for an internal supply voltage as well as driver circuits. Each of the driver circuits has an associated data connecting pad and a respective output which is connected to the associated data connecting pad. The semiconductor module which, for example, is in the form of a memory chip is, for example, contained in an x16 housing configuration and is usable in an x4 or x8 module configuration, in which the other pads (I/Os 9 to 16) are not connected to the housing. The x4 and x8 module configurations are used in particular in so-called high-end systems.
According to the invention, one of the data connecting pads, which is not used for interchanging data or commands during operation of the semiconductor module, is permanently connected to the connection for the internal supply voltage for the semiconductor module. It is thus possible, using previous housing forms, to achieve a reduced inductance in the current path of the data lines when only one x4 and x8 module configuration is used. This makes it possible to use a higher clock frequency on the data lines, and hence to achieve an increased data rate.
One input of one of the driver circuits, whose output is connected to one of the data connecting pads, is advantageously permanently connected to a further connection for a supply voltage for the semiconductor module.
In one embodiment of the semiconductor module according to the invention, one of the data connecting pads and/or the input of the driver circuit which is connected to that data connecting pad are/is connected to the respective connection via a closed switch in the form of a so-called on-chip metal option. These metal options form simple switches.
Since, in principle, the invention can be used independently of the mounting technology that is used, it is also possible, provided there are a sufficient number of connecting pins, to implement logic switches via which one of the connecting pads and/or the input of the driver circuit which is connected to that connecting pad are/is connected to the respective connection. A logic switch such as this advantageously has an external connection, via which the logic switch can be controlled. The external connection is, for example, connected to the exterior as an additional connecting pin, thus allowing external control of the circuitry of an unused data connecting pad for the additional power supply.
In accordance with an added feature of the invention, an additional connection for receiving an externally supplied supply voltage is provided, and one of the data connecting pads is permanently connected to the additional connection. The additional connection for the externally supplied supply voltage is a ground connection.
In accordance with a further feature of the invention, a switching transistor is provided that is permanently switched on. The output of one of the driver circuits is connected to the connection for the internal supply voltage through the switching transistor.
With the foregoing and other objects in view there is provided, in accordance with the invention, a housing configuration. The housing configuration includes a semiconductor module containing data connecting pads, driver circuits each having an output connected to an associated one of the data connecting pads, and a connection for receiving an internal supply voltage for the semiconductor module. At least one of the data connecting pads not being used for interchanging data or commands during operation of the semiconductor module is permanently connected to the connection. A mounting substrate is provided and the semiconductor module is disposed on the mounting substrate. The mounting substrate has a contact hole for making contact with an externally supplied supply voltage. A resistor link is provided and connecting pins extend from the semiconductor module. One of the connecting pins is connected to the data connecting pad not being used for interchanging data or commands during operation of the semiconductor module. The connecting pin and the contact hole are fitted with the resistor link. The resistor link short-circuits the data connecting pad and the contact hole.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor module having a configurable data width of an output bus, and a housing configuration having a semiconductor module, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.